14- Diffusion of Gases in the Lung

Question 1

what happens when you have two time constants for each lung?

Answer 1

non-uniform distribution in the lungs and one lung (the slower one) does not get as much fresh air cause it ends up getting some of the old air from the faster working lung

Question 2

what determines movement of gases

Answer 2

pressure gradients (differences)

Question 3

gas pressure

Answer 3

force created when gas molecules strike an object which is determined by density of molecules and temperature

Question 4

how to calculate partial pressures

Answer 4

from fractional concentration and total pressure

Question 5

why is water vapor pressure important?

Answer 5

air is saturated with water before entry to alveoli

-water vapor pressure at body temp is 47 mmHg

Question 6

Henrys Law

Answer 6

concentration of gas in a liquid

= gas x solubility coefficient

solubility coefficient is the “attractiveness of a gas”

Question 7

what happens to capillaries as you increase lung volume

Answer 7

capillaries get smaller so resistance to flow increases as lung volume increases

• to increase lung volume you need to create a more and more negative pleural pressure which causes veins/arteries to dilate which causes their resistance to decrease
• pulmonary capillaries are embedded in the space between adjacent alveoli

Question 8

Pathway of gas diffusion in the lung

Answer 8

a) Water and surfactant in the alveoli
b) Alveolar epithelium
c) Epithelial basement membrane
d) Interstitial fluid space

e) Capillary basement
membrane

f) Capillary endothelium and
g) Plasma to reach the red cell membrane

Question 9

oxygen diffusion order and diffusion relations

Answer 9

oxygen diffuses from alveoli to capillaries and binds to hemoglobin

• diffusion is directly related to pressure gradient, surface area, and gas solubility
• diffusion is inversely related to diffusion distance and gas molecular weight
• pressure gradient, surface area, and distance are determined by the membrane
• gas solubility and molecular weight are characteristics of the gas and determine the diffusion coefficient

Question 10

Lung Diffusing Capacity (DL)

Answer 10

-calculated as gas uptake/average pressure gradient for diffusion

BUT WE ACTUALLY USE THE FOLLOWING TO ESTIMATE THE MEASUREMENTS

• lung diffusing capacity is estimated measuring uptake of CO
• due to rapid CO uptake by hemoglobin, PC remains at zero; thus DL = CO uptake/PACO

Question 11

O2 rate of equilibration

Answer 11

• rate of equilibration of O2 between alveoli and pulmonary capillaries
• Note there is an increased equilibration time when DL is below normal

Question 12

CO2 rate of equilibration

Answer 12

• rate of equilibration of CO2 between alveoli and pulmonary capillaries
• in comparison to previous slide equilibration time is greater for CO2 than for O2, but CO2 is affected relatively less by a reduced DM

Question 13

rate of alveolar-capillary diffusion

Answer 13

• exercise reduces pulmonary transit time, so if diffusion is sufficiently abnormal then equilibrium between alveoli and capillaries will not be reached
• rate of equilibration between alveoli and capillaries is reduced during hypoxia

Question 14

Pneumonia and emphysema

Answer 14

• decrease diffusion in the lung
• pneumonia: fluid and blood cells in the alveoli so O2 cant get in as easily
• emphysema: reduction in surface area cause the alveoli shrink

Question 15

list the conditions that affect diffusion in the lung

Answer 15

1. emphysema
2. pneumonia/pulmonary edema
3. pulmonary fibrosis
4. exercise
5. acute hypoxia
6. Acute Respiratory distress syndrome (ARDS)

Question 16

emphysema and diffusion in lung

Answer 16

• coalescence of alveoli decreases surface area and thus DL
• irreversible
• causes hypoxemia

Question 17

pneumonia/pulmonary edema and diffusion in lung

Answer 17

• fluid in interstitial space and alveoli decreases diffusion
• reversible
• causes hypoxemia

Question 18

pulmonary fibrosis and diffusion in lung

Answer 18

• thickened alveolar-capillary membranes decrease DL
• irreversible
• causes hypoxemia

Question 19

exercise and diffusion in lung

Answer 19

increases due to expansion of pulmonary capillaries to increase surface area

Question 20

acute hypoxia and diffusion in lung

Answer 20

diffusion decreases due to decreased pressure gradient (so less driving pressure)

Question 21

acute respiratory distress syndrome and diffusion in lung

Answer 21

1) acute, diffuse, inflammatory lung injury,
2) pneumonia, sepsis, aspiration of gastric contents, and trauma
3) diffuse alveolar damage including inflammatory infiltrates in the alveolar walls, interstitial edema, and a proteinaceous film lining the alveoli.
4) endothelial barrier breaks down, allowing fluid to leak into alveoli
5) endothelium expresses adhesion molecules that bind leukocytes, enabling leukocytes movement into alveoli to release mediators damaging the alveoli
6) epithelial cells stop pumping fluid out of the alveoli.
7) 190,000 ARDS cases in the USA each year, mortality rate of 40%.

Question 22

high altitudes and diffusion in the lung

Answer 22

• Residence during childhood stimulates lung growth increasing surface area to increase DL (increases diffusion)
• stimulus of hypoxia causes lung growth
• this is only short term but something before a marathon people sleep in a hypoxic tent so they can increase Hb levels and maybe do better the day of the run but eventually it goes back down to normal when your body is in a normal area

Question 23

gas exchange between systemic capillaries and tissues by diffusion

Answer 23

• oxygen is released from hemoglobin and then diffuses into the tissues
• Note: CO2 transport is primarily as HCO3-
• passive diffusion: O2 needs to diffuse from the Hb before it can have the kinetic energy to go into the tissues and same but opposite for CO2

Question 24

changes in lung volume can affect

Answer 24

diameter of airways

Question 25

during exhalation below FRC

Answer 25

airways are compressed

Question 26

emphysema affects airway diameter b/c…

Answer 26

due to loss of elasticity keeping the airway expanded

Question 27

asthma affects airway diameter b/c…

Answer 27

cause of contraction of the smooth muscle

Question 28

one thing that affects airway diameter

Answer 28

transmural pressure (differences in pressure b/w inside and outside of airway)

Question 29

what may result when airway time constants are not uniform and breathing frequency is high

Answer 29

hypoxemia

Question 30

characteristic of healthy human seated in chair

Answer 30

alveolar pressure will be sub-atomspheric only during inspiration